Magnetic intermetallic compound interconnect

ABSTRACT

The present disclosure relates to the field of fabricating microelectronic packages, wherein magnetic particles distributed within a solder paste may be used to form a magnetic intermetallic compound interconnect. The intermetallic compound interconnect may be exposed to a magnetic field, which can heat a solder material to a reflow temperature for attachment of microelectronic components comprising the microelectronic packages.

RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 12/768,842, filed on Apr. 28, 2010, entitled “MAGNETIC INTERMETALLICCOMPOUND INTERCONNECT”.

BACKGROUND

A typical microelectronic package includes at least one microelectronicdie that is mounted on a substrate such that bond pads on themicroelectronic die are attached directly to corresponding bond lands onthe substrate using reflowable solder balls.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification.The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. It is understoodthat the accompanying drawings depict only several embodiments inaccordance with the present disclosure and are, therefore, not to beconsidered limiting of its scope. The disclosure will be described withadditional specificity and detail through use of the accompanyingdrawings, such that the advantages of the present disclosure can be morereadily ascertained, in which:

FIGS. 1-8 illustrate side cross-sectional views of a process of formingmagnetic intermetallic compound interconnects on a substrate and theattachment of a microelectronic die to the substrate;

FIGS. 9-11 illustrate side cross-sectional views of a process of formingmagnetic intermetallic compound interconnects on a microelectronic dieand the attachment of a microelectronic device to the microelectronicdie;

FIGS. 12-16 illustrate side cross-sectional views of a process offorming magnetic intermetallic compound interconnects on a firstmetallic attachment structure and the attachment of a second metallicattachment structure to the first metallic attachment structure; and

FIG. 17 is a flow diagram of a process of forming magnetic intermetalliccompound interconnects on a first metallic attachment structure and theattachment of a second metallic attachment structure to the firstmetallic attachment structure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the claimed subject matter may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the subject matter. It is to be understood thatthe various embodiments, although different, are not necessarilymutually exclusive. For example, a particular feature, structure, orcharacteristic described herein, in connection with one embodiment, maybe implemented within other embodiments without departing from thespirit and scope of the claimed subject matter. In addition, it is to beunderstood that the location or arrangement of individual elementswithin each disclosed embodiment may be modified without departing fromthe spirit and scope of the claimed subject matter. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the subject matter is defined only by the appendedclaims, appropriately interpreted, along with the full range ofequivalents to which the appended claims are entitled. In the drawings,like numerals refer to the same or similar elements or functionalitythroughout the several views, and that elements depicted therein are notnecessarily to scale with one another, rather individual elements may beenlarged or reduced in order to more easily comprehend the elements inthe context of the present description.

Embodiments of the present description relate to the field offabricating microelectronic packages, wherein magnetic particlesdistributed within a solder paste may be used to form a magneticintermetallic compound interconnect. The intermetallic compoundinterconnect may be exposed to a magnetic field, which can heat a soldermaterial to a reflow temperature for attaching microelectroniccomponents comprising the microelectronic package.

In the production of microelectronic packages, microelectronic dice aregenerally mounted on substrates that may in turn be mounted to boards,which provide electrical communication routes between themicroelectronic die and external components. A microelectronic die, suchas a microprocessor, a chipset, a graphics device, a wireless device, amemory device, an application specific integrated circuit, or the like,may be attached to a substrate, such as an interposer, a motherboard,and the like, through a plurality of interconnects, such as reflowablesolder bumps or balls, in a configuration generally known as a flip-chipor controlled collapse chip connection (“C4”) configuration. When themicroelectronic die is attached to the substrate with interconnects madeof solder, the solder is reflowed (i.e. heated) to secure the solderbetween the microelectronic die bond pads and the substrate bond pads.

During such an attachment, a thermal expansion mismatch may occurbetween the microelectronic die and the substrate as the solder isheated to a reflow temperature and subsequently cooled after theattachment. This thermal expansion mismatch can warp the microelectronicpackage, as well as cause significant yield losses and failures due to,for example, stretched joint formation, solder bump cracking, under bumpmetallization failures, edge failures, and layer separation within thesubstrates and microelectronic dice, as will be understood to thoseskilled in the art.

FIGS. 1-8 illustrate an embodiment of using a magnetic material tolocally heat interconnects according to one embodiment of the presentdisclosure. FIG. 1 shows a substrate 102 having at least one attachmentstructure, such as bond pads 104, formed therein. The substrate 102 maybe primarily composed of any appropriate material, including, but notlimited to, bismaleimine triazine resin, fire retardant grade 4material, polyimide materials, glass reinforced epoxy matrix material,and the like, as well as laminates or multiple layers thereof. Thesubstrate bond pads 104 may be composed of any conductive metal,including but not limited to, copper, aluminum, and alloys thereof. Thesubstrate bond pads 104 may be in electrical communication withconductive traces (not shown) within the substrate 102.

Each substrate bond pad 104 may optionally include a finish layer 106formed thereon. The finish layer 106 may be used to prevent oxidation ofthe substrate bond pad 104 and/or to increase the adhesion between thesubstrate bond pad 104 and a subsequently formed interconnect, as willbe discussed. The finish layer 106 may include gold, nickel, copper,palladium, indium, and silver, and alloys thereof. In one embodiment,the finish layer 106 may be a single metal layer, such as layer of gold,which may be formed by a direct immersion gold process. In anotherembodiment, the finish layer 106 may be a metal alloy layer, such as anickel/palladium/gold alloy, an indium/silver alloy, or variouscopper-based alloy surface finishes. In yet another embodiment, thefinish layer 106 may be multiple layers of metals, such as a layer ofgold on a layer of nickel, which may be formed by an electrolessnickel/immersion gold (“ENIG”) plating method followed by an electrolessgold (“EG”) plating method, as will be understood to those skilled inart.

An outer dielectric layer 112 may be formed adjacent the substrate 102and the substrate bond pads 104, wherein openings 108 extend through theouter dielectric layer 112 to expose a portion of each of the substratebond pads 104. The outer dielectric layer 112 may be a solder resistmaterial, including but not limited to epoxy and epoxy-acrylate resins.The substrate 102, substrate bond pad 104, and the outer dielectriclayer 112 may be formed by any known techniques, as will be understoodby those skilled in the art.

A magnetic composite material 114 may be deposited adjacent to thesubstrate bond pads 104, as shown in FIG. 2. As illustrated, themagnetic composite material 114 is deposited on the finish layer 106.The magnetic composite material 114 may comprise magnetic particlesdispersed in a solder paste. In one embodiment, the magnetic compositematerial 114 may contain between about 1% and 10% by weight of magneticparticles. In another embodiment, the magnetic composite material 114may have magnetic particles sized between about 5 and 100 nm in length.The magnetic composite material 114 may be deposited by any knowntechnique including printing and spraying, and may be deposited to athickness of between about 1 and 3 microns.

The magnetic particles may include, but are not limited to, iron (Fe),cobalt (Co), nickel (Ni), and their respective alloys. Examples may alsoinclude ferrites and oxides containing magnetic metals. In oneembodiment, the magnetic particles may be MFe₂O₄, where M may be anymetal and O is oxygen. In another embodiment, the magnetic particles maybe BaFe₁₂O₁₇, where Ba is barium. In yet another embodiment, themagnetic particles may comprise an iron/cobalt alloy. In certainembodiments, the magnetic particles may include a coating such as aconformal tin (Sn)/tin-based alloy/copper (Cu) layer formed, forexample, by a deposition procedure, such as sputtering. The coating isdesigned to promote desirable wetting between the molten (reflowed)solder of subsequently formed solder interconnect bumps (as will bediscussed) and the magnetic particles.

The solder paste may be any appropriate material, including but notlimited to lead/tin alloys, such as 63% tin/37% lead solder, orlead-free solders, such a pure tin or high tin content alloys (e.g. 90%or more tin), such as tin/bismuth, eutectic tin/silver, ternarytin/silver/copper, eutectic tin/copper, and similar alloys. In oneembodiment, the solder paste is a tin/silver solder.

As shown in FIG. 3, a mask 122 may be placed the outer dielectric layer112 and a solder material 124 may be deposited in the openings 108 (seeFIGS. 1 and 2) by a printing technique. The solder material 124 may beany appropriate material, including but not limited to lead/tin alloys,such as tin/lead solder, or lead-free solders, such a pure tin or hightin content alloys, such as tin/bismuth, eutectic tin/silver, ternarytin/silver/copper, eutectic tin/copper, and similar alloys. The mask 122may then be removed, as shown in FIG. 4. It is understood that thesolder material 124 could be deposited by other techniques, includingbut not limited to spraying techniques.

The solder material 124 could be heated with an external heat source toa reflow temperature to form solder interconnect bumps and form anintermetallic compound interconnect between the substrate bond pads 104and the solder material 124 for adhesion therebetween. However, oneissue with such reflow heating is the non-uniformity of the heatingrates across multiple solder interconnect bumps, resulting in differingintermetallic compound growth, as well as different texturing of thesolder materials, as will be understood those skilled in the art.

A magnetic field generator 132, as shown in FIG. 5, may be placedproximate the assembly 130 of FIG. 4. In the presence of alternatingcurrent magnetic fields generated by the magnetic field generator 132,the magnetic particles within the magnetic composite material 114 willgenerate heat by relaxational and hysteretic loss modes. Relaxationallosses occur in single domain magnetic particles and they release heatwhen the magnetic moment of the particle rotates with the appliedmagnetic field (Neel motion) and when the particle itself rotates due toBrownian motion. Hystereis losses occur in multi-domain particles, andgenerate heat due to the various magnetic moments (due to multi-domains)rotating against the applied magnetic field. These losses occur withevery cycle in the alternating current field, and the net heat generatedincreases with increasing number of field cycles. The various factorscontrolling heating rates may include, but are not necessarily limitedto, magnetic particle size and size distribution, magnetic particlevolume fractions (heat generation scales substantially linearly withvolume fraction), magnetic material choice (oxides, metallic (pure andalloy), and layered magnetic particles (as previously discussed)), shapeanisotropy of the magnetic particle, and the applied frequency andamplitude of the alternating current used in the magnetic fieldgenerator 132. Therefore, as shown in FIG. 5, when an alternatingcurrent magnetic field is applied by the magnetic field generator 132,the magnetic particles within the magnetic composite material 114essentially vibrate and heat up to at least the reflow temperature ofthe solder material 124, thereby forming substrate interconnection bumps126 and magnetic intermetallic compound interconnects 128. The magneticintermetallic compound interconnects 128 may comprise the magneticcomposite material 114, at least a portion of the finish layer 106, anda portion of the solder material 124, which diffuse into one anotherduring heating. The magnetic intermetallic compound interconnect 128adheres the substrate bond pad 104 to the solder material 124, as willbe understood to those skilled in the art.

The use of the magnetic composite material 114 and the magnetic fieldgenerator 132 to form the magnetic intermetallic compound interconnects128 may substantially reduce thermal mass variations in comparison tousing an external heat source, and thereby may substantially reducedifferences in intermetallic compound growth and/or different texturingof the solder materials, which may result in more reliable andpredictable connections between microelectronic devices, as will bediscussed. Furthermore, the use of the magnetic composite material 114and the magnetic field generator 132 result in the formation themagnetic intermetallic compound interconnects 128 being dependent on thethickness of the magnetic composite material 114 and on the magneticfield generated by the magnetic field generator 132, as will beunderstood by those skilled in the art, which may improve control of theprocess.

It is understood that a number of variations of the present disclosuremay be used. In one variation, the magnetic composite material 114 maybe disposed only on selected substrate bond pads 104 and a magneticfield generator 132 may be used in conjunction with an external heatsource (not shown) to form the solder interconnect bumps 126.

The magnetic intermetallic compound interconnects 128 of FIGS. 4 and 5may be used to attach microelectronic devices or component to oneanother. FIGS. 6-8 illustrate the attachment of a microelectronic die toa substrate. As shown in FIG. 5, a microelectronic device 134, such as amicroelectronic die or an interposer, may be provided having at leastone attachment mechanism, such as at least on attachment projection 136on a first surface 142 thereof. The attachment projections 136 may beany appropriate metal material, including but not limited to copper andalloys thereof. A pattern or distribution of the microelectronic dieattachment projections 136 may be a substantial mirror-image to thepattern or distribution of the substrate interconnection bumps 126. Themagnetic field generator 132 may then be activated to heat the magneticcomposite material 114, which, in turn, brings the solderinterconnection bumps 126 to their reflow temperature. As shown in FIG.7, the microelectronic die attachment projections 136 may be insertedinto their respective reflowed solder interconnection bumps 126. Themagnetic field generator 132 may then be deactivated, or the substrateand the attached microelectronic die 134 may be removed from themagnetic field, which allows the solder interconnection bumps 126 tocool and re-solidify, as shown in FIG. 8.

Since the heating to reflow of the solder interconnection bumps 126during the attachment to the microelectronic device 134 is localizedproximate the magnetic intermetallic compound interconnects 128, othercomponents (layer, traces, and the like) in the substrate are onlyminimally heated up by the magnetic field relative to external heatingtechniques. Thus, the magnetic heating of the present disclosureminimizes stresses due to thermal expansion mismatch.

Another embodiment of the subject matter of the present description isshown in FIGS. 9 and 10, wherein solder interconnection bumps are formedon a microelectronic die. FIG. 9 illustrates a microelectronic die 200,such as a microprocessor, a chipset, a graphics device, a wirelessdevice, a memory device, an application specific integrated circuit, orthe like. The microelectronic die 200 may comprises first dielectriclayer 202 with bond pads 204 formed thereon. An outer dielectric layer206 may be formed over the first dielectric layer 202 and themicroelectronic die bond pads 204. The microelectronic die bond pads 204may be metal, including but not limited to, copper, silver, aluminum,gold, and alloys thereof. The microelectronic die bond pads 204 may bein electrical communication with conductive traces (not shown) withinthe microelectronic die 200. The first dielectric layer 202, themicroelectronic die bond pads 204, and the outer dielectric layer 206may be formed by any known techniques, as will be understood by thoseskilled in the art.

An optional conductive adhesion layer 212, such as titanium and alloysthereof, may be formed adjacent the microelectronic die bond pad 204.The conductive adhesion layer 212 may be formed by any known depositiontechnique, including but not limited to, chemical vapor deposition,atomic layer deposition, physical vapor deposition, plating, and thelike.

The first dielectric layer 202 and/or the outer dielectric layer 206 maybe a silicon oxide, silicon nitride, or low-K dielectric material (i.e.dielectric materials with a dielectric constant “K” lower than that ofsilicon oxide), including but not limited to carbon doped silicondioxide and fluorine doped silicon dioxide. The outer dielectric layer206 may also be a solder resist material, including but not limited to,epoxy and epoxy-acrylate resin.

A magnetic composite material 214, such as described with regard toFIGS. 2-4, may be formed adjacent the microelectronic die bond pad 204.As shown in FIG. 9, the magnetic composite material 214 may be formed onthe conductive adhesion layer 212, and a solder material 216 depositedin openings (not shown) through the outer dielectric layer 206, similarto that described with regard to FIGS. 3 and 4.

As shown in FIG. 10, a magnetic field generator 232 may be placedproximate the microelectronic die 200 of FIG. 9. An alternating currentmagnetic field may then be applied by the magnetic field generator 232,the magnetic particles within the magnetic composite material 214vibrate and heat up to at least the reflow temperature of the soldermaterial 216, thereby forming magnetic intermetallic compoundinterconnects 228 and microelectronic die interconnection bumps 226.

As shown in FIG. 11, a microelectronic device 234, such as an interposeror substrate, having a plurality of bond pads 236 on a first surface 242thereof may be attached to the microelectronic die 200. A pattern ordistribution of the microelectronic device bond pads 236 may be asubstantial mirror-image to the pattern or distribution of themicroelectronic die interconnection bumps 226. The magnetic fieldgenerator 232 may be activated to heat the magnetic intermetalliccomposite material 214, which, in turn, brings the solder material 216to at least its reflow temperature. The microelectronic device bond pads236 are brought into contact their respective reflowed microelectronicdie solder interconnection bumps 226. The magnetic field generator 232may then be deactivated, or the microelectronic die 200 and themicroelectronic device 234 may be removed from the magnetic field, whichallows the microelectronic die solder interconnection bumps 226 to cooland re-solidify to attach the microelectronic die 200 to themicroelectronic device 234.

It is understood that the concepts of the present description apply toany microelectronic packaging process, including but not limited toFirst Level Interconnects (FLI) where microelectronic dice are attachedto substrates or interposers, to Second Level Interconnects (SLI) wheresubstrates or interposers are attached to a board or a motherboard, andto Direct Chip Attach (DCA) where microelectronic dice are attacheddirectly attached to a board or a motherboard.

It is understood that the subject matter of the present description isnot necessarily limited to specific applications illustrated in FIGS.1-11. The subject matter may be applied to other solder attachmentprocesses in the fabrication of microelectronic devices, including, butnot limited to, attachment of electronic devices to a motherboard,attachment of integrated heat spreaders, and the like. Furthermore, thesubject matter may also be used in any appropriate solder attachmentapplication outside of the microelectronic device fabrication field.

An embodiment of a process of the present description is illustrated inFIGS. 12-16 and in the flow diagram 400 of FIG. 17. As shown in FIG. 12and defined in block 410 of FIG. 17, a first metallic attachmentstructure 302 may be provided. The first metallic attachment structure302 may be any appropriate structure, including, but not limited to, thesubstrate bond pad 104 of FIGS. 1-8 and the microelectronic die bond pad204 of FIGS. 9-11. A magnetic composite material 304, such as previouslydescribed, may be deposited adjacent the first metallic attachmentstructure 302, as shown in FIG. 13 and defined in block 420 of FIG. 17.A solder material 306, such as previously described, may be depositedadjacent the magnetic composite material 304, as shown in FIG. 14 anddefined in block 430 of FIG. 17. The solder material 306 may reflowed inan alternating current magnetic field that may be generated with amagnetic field generator 312 proximate the magnetic composite material304, which forms a magnetic intermetallic compound 314, as shown in FIG.15 and defined in block 440 of FIG. 17. As shown in FIG. 16 and definedin block 450 of FIG. 17, a second metallic attachment structure 316 maybe brought into contact with the reflowed solder material 306. Thesecond metallic attachment structure 316 may be any appropriatestructure, including, but not limited to the microelectronic dieattachment projections 136 of FIGS. 6-8 and the microelectronic devicebond pads 236 of FIG. 11.

The detailed description has described various embodiments of thedevices and/or processes through the use of illustrations, blockdiagrams, flowcharts, and/or examples. Insofar as such illustrations,block diagrams, flowcharts, and/or examples contain one or morefunctions and/or operations, it will be understood by those skilled inthe art that each function and/or operation within each illustration,block diagram, flowchart, and/or example can be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof.

The described subject matter sometimes illustrates different componentscontained within, or connected with, different other components. It isunderstood that such illustrations are merely exemplary, and that manyalternate structures can be implemented to achieve the samefunctionality. In a conceptual sense, any arrangement of components toachieve the same functionality is effectively “associated” such that thedesired functionality is achieved. Thus, any two components hereincombined to achieve a particular functionality can be seen as“associated with” each other such that the desired functionality isachieved, irrespective of structures or intermediate components.Likewise, any two components so associated can also be viewed as being“operably connected”, or “operably coupled”, to each other to achievethe desired functionality, and any two components capable of being soassociated can also be viewed as being “operably couplable”, to eachother to achieve the desired functionality. Specific examples ofoperably couplable include but are not limited to physically mateableand/or physically interacting components and/or wirelessly interactableand/or wirelessly interacting components and/or logically interactingand/or logically interactable components.

It will be understood by those skilled in the art that terms usedherein, and especially in the appended claims are generally intended as“open” terms. In general, the terms “including” or “includes” should beinterpreted as “including but not limited to” or “includes but is notlimited to”, respectively. Additionally, the term “having” should beinterpreted as “having at least”.

The use of plural and/or singular terms within the detailed descriptioncan be translated from the plural to the singular and/or from thesingular to the plural as is appropriate to the context and/or theapplication.

It will be further understood by those skilled in the art that if anindication of the number of elements is used in a claim, the intent forthe claim to be so limited will be explicitly recited in the claim, andin the absence of such recitation no such intent is present.Additionally, if a specific number of an introduced claim recitation isexplicitly recited, those skilled in the art will recognize that suchrecitation should typically be interpreted to mean “at least” therecited number.

The use of the terms “an embodiment,” “one embodiment,” “someembodiments,” “another embodiment,” or “other embodiments” in thespecification may mean that a particular feature, structure, orcharacteristic described in connection with one or more embodiments maybe included in at least some embodiments, but not necessarily in allembodiments. The various uses of the terms “an embodiment,” “oneembodiment,” “another embodiment,” or “other embodiments” in thedetailed description are not necessarily all referring to the sameembodiments.

While certain exemplary techniques have been described and shown hereinusing various methods and systems, it should be understood by thoseskilled in the art that various other modifications may be made, andequivalents may be substituted, without departing from claimed subjectmatter or spirit thereof. Additionally, many modifications may be madeto adapt a particular situation to the teachings of claimed subjectmatter without departing from the central concept described herein.Therefore, it is intended that claimed subject matter not be limited tothe particular examples disclosed, but that such claimed subject matteralso may include all implementations falling within the scope of theappended claims, and equivalents thereof.

What is claimed is:
 1. A microelectronic interconnection, comprising: afirst metallic attachment structure; a magnetic composite materialadjacent the first metallic attachment structure; and a solder materialadjacent the magnetic composite material.
 2. The microelectronicinterconnection of claim 1, wherein the magnetic composite materialcomprises magnetic particles dispersed in a solder paste.
 3. Themicroelectronic interconnection of claim 2, wherein the magneticparticles comprises iron, cobalt, nickel, or alloys thereof.
 4. Themicroelectronic interconnection of claim 3, wherein the magneticparticles comprise an iron and cobalt alloy.
 5. The microelectronicinterconnection of claim 2, wherein the solder paste comprises a tin andsilver solder paste.
 6. The microelectronic interconnection of claim 1,wherein the first metallic attachment structure comprises a firstmetallic attachment structure disposed on a microelectronic substrate.7. A microelectronic interconnection, comprising: a first metallicattachment structure on a substrate; a dielectric layer over thesubstrate and the first metallic attachment structure, wherein thedielectric layer has an opening therethrough to a portion of the firstmetallic attachment structure; a magnetic composite material adjacentthe first metallic attachment structure within the dielectric layeropening; and a solder material adjacent the magnetic composite materialwithin the dielectric layer opening.
 8. The microelectronicinterconnection of claim 7, wherein the magnetic composite materialcomprises magnetic particles dispersed in a solder paste.
 9. Themicroelectronic interconnection of claim 8, wherein the magneticparticles comprises iron, cobalt, nickel, or alloys thereof.
 10. Themicroelectronic interconnection of claim 8, wherein the magneticparticles comprises an iron and cobalt alloy.
 11. The microelectronicinterconnection of claim 8, wherein the solder paste comprises a tin andsilver solder paste.
 12. A microelectronic package, comprising: a firstmetallic attachment structure on a substrate; a dielectric layer overthe substrate and the first metallic attachment structure, wherein thedielectric layer has an opening therethrough to expose a portion of thefirst metallic attachment structure; a magnetic composite materialadjacent the first metallic attachment structure within the dielectriclayer opening; a solder material adjacent the magnetic compositematerial within the dielectric layer opening; and a microelectronicdevice having at least one attachment projection attached to the soldermaterial.
 13. The microelectronic package of claim 12, wherein themagnetic composite material comprises magnetic particles dispersed in asolder paste.
 14. The microelectronic package of claim 13, wherein themagnetic particles comprise iron, cobalt, nickel, or alloys thereof. 15.The microelectronic package of claim 13, wherein the magnetic particlescomprise an iron and cobalt alloy.
 16. The microelectronic package ofclaim 13, wherein the solder paste comprises a tin and silver solderpaste.